KR20190053772A - Vibrating structure gyroscopes - Google Patents

Abstract

A vibration structure gyroscope comprises: an annular resonator (6) arranged so as to vibrate in a plane in response to electrostatic driving forces; a first set of capacitive balancing electrodes (8) which are digitally controlled; and a second set of capacitive balancing electrodes (10) which are digitally controlled. The second set of capacitive balancing electrodes (10) are arranged to dynamically apply a micro balancing voltage which generates a dynamic electrostatic balancing force.

Description

VIBRATING STRUCTURE GYROSCOPES [0002]

This disclosure relates to a vibrating structure gyroscope, and more particularly, but not exclusively, to a Coriolis-type gyroscope.

Vibration structure gyroscopes fabricated using Micro-Electro-Michanical Systems (MEMS) technology can find applications in aerospace applications for guidance and control. A typical Coriolis-type oscillating structure gyroscope includes an annular resonator supported by compliant legs for in-plane oscillation in response to electrostatic drive signals. The annular resonator can be operated using a cos 2 &thetas; pair of vibrations, for example, as described in WO 2006/006597. In operation, the drive transducer excites the first carrier oscillation along the main movement axis at a nominal resonance frequency, e.g., 14 kHz. When the gyroscope is rotated about the normal axis in the plane of the annular resonator, the Coriolis force is generated to couple the energy with the secondary response oscillation along the secondary axis of movement, which is located at 45 degrees to the primary axis. In the theoretical case of a perfect annular resonator, the main movement, schematically shown in Fig. 1, is always aligned with the main axis regardless of excitation frequency. Coriolis-induced secondary response vibration is aligned at 45 degrees on the secondary axis and there is no frequency division.

In practice, however, the annular shape of the resonator is geometrically imperfect, which means that the first carrier oscillation at a given resonant frequency (e.g., 14 kHz) is in two orthogonal modes, a high frequency mode shifted to a slightly higher frequency f _H HFM) and a slightly lower frequency f _L shifted low frequency mode (LFM). Since incompleteness leads to modes with different frequencies, one is inevitably higher frequency than the other. However, the high frequency mode f _H may or may not be higher than the perfect case where the mode frequencies are the same. The frequency division Δf is the difference between the frequencies of HFM and LFM, ie Δf = f _H -f _L. For a cos 2 &thetas; pair, the orthogonal high frequency and low frequency modes are always at 45 degrees relative to each other, but may be at any angular position relative to the major axis used as the reference axis in general. The angle value? Depends on the imperfection in the resonator.

MEMS design and fabrication processes can produce planar silicon ring resonators with precise tolerances as an attempt to minimize any frequency difference between high and low frequency modes. However, small imperfections in the geometry of the annular resonator will also typically result in residual frequency division.

The performance of a MEMS ring gyroscope can be improved by more accurate balancing of high frequency and low frequency modes than can be achieved at the time of manufacture. In one approach, the mass or stiffness distribution of the annular resonator is adjusted, for example, using laser ablation of material after fabrication. Laser balancing, as described in WO 2013/136049, is generally used as part of the production process for inductive gyroscopes. This provides improved performance but can not account for any changes in operation and lifetime.

In a capacitive gyroscope, electrostatic balancing schemes can typically resolve balancing for any position around the ring using a plurality of balancing electrode plates disposed around the annular resonator. The initial static electrostatic balancing correction may be applied to one or more plates to locally adjust the stiffness of the annular resonator and to compensate for manufacturing tolerances. However, it is also known to control electrostatic balancing voltages during operation. For example, WO 2006/006597 describes 16 balancing electrode plates used for oscillating frequency adjustment during operation of a gyroscope. Electrostatic balancing applies a local reduction of stiffness which results in a frequency reduction proportional to the square of the voltage difference between the ring and the balancing plate. This means that the high frequency and low frequency modes can be adjusted differently to try to achieve an exact match. By applying the fixed DC voltages to a group of four balancing plates located around the annular resonator, the frequency division [Delta] f can be reduced to less than 1 Hz. 2 is an example of a 33,000 Q factor gyroscope (a = 0 degrees) with a 0.424 Hz division between HFM and LFM frequencies.

Although the electrostatic balancing has been used in capacitive gyroscopes, the digitally-controlled voltages applied to the balancing plates are divided into a digital-to-analog converter (DAC) and a discrete set by its defined least significant bit (LSB) Discrete analog output values, i.e., steps between successive analog outputs. When using digital means of linearly varying voltage, the resolution of the balancing effect decreases as the applied voltage difference increases. This is due to the square nature of the balancing, with frequency division [Delta] f being related to the square of the voltage. When dynamic balancing is performed in conjunction with large static balancing correction, the available resolution is degraded, which limits the performance of the overall gyroscope.

There is still a need to achieve improved electrostatic frequency balancing during operation of capacitive gyro spokes.

Wherein a vibrating structural gyroscope is disclosed comprising:

An annular resonator arranged to vibrate in plane in response to the electrostatic driving forces;

A first frequency from f _P along the primary by here a first cos nθ resonance, the Coriolis force resulting from the applied angular rate about the out-of-plane (out-of-plane) axes claim along the second in a second frequency f _S 2 a set of capacitive driving electrodes arranged to apply a voltage to induce cos n? resonance, which generates an electrostatic driving force;

The geometry of the annular resonator is superimposed on the high frequency mode f _H and the orthogonal low frequency mode f _L , resulting in a first frequency f _P having a frequency division? F defined by? F = f _H -f _L ,

A first static balancing to generate a static electrostatic balancing force to lower the frequency f _H by an offset frequency f _H 'below the frequency f _L by a small frequency offset f ₀ , i.e., f _H ' = f _H -? F - f ₀ , A first digitally controlled set of capacitive balancing electrodes arranged to apply a voltage; And

To apply a second static balancing voltage that produces a small static electrostatic balancing force to lower the frequency f _L by an offset frequency f _L ', i.e., f _L ' = f _L -f ₀ , by the same small frequency offset f ₀ And a second digitally controlled second set of capacitive balancing electrodes disposed,

Capacitive balancing electrode of the second set of fine balancing voltage for generating a dynamic electrostatic balancing force to provide fine frequency adjustment ± δf to reduce the offset frequency f _H, so as to keep "a f _L 'during operation f _H in As shown in FIG.

In practice, it will be appreciated that the incomplete geometry of the annular resonator unfortunately results in the first frequency f _p being superimposed on the high frequency mode f _H and the orthogonal low frequency f _L. The low-frequency mode f _L is mathematically orthogonal, that is, in an anti-node position when compared to the node position of the high-frequency mode f _H. There is an angle of 45 degrees between the high frequency mode f _H and the orthogonal low frequency mode f _L for the first cos 2? Resonance. There is an angle of 30 degrees between the high frequency mode f _H and the orthogonal low frequency mode f _L for the first cos 3? Resonance. Of course higher order cos n? Resonances can be excited, and the angle between the high frequency mode f _H and the orthogonal low frequency mode f _L is given by the general rule of 90 ° / n.

According to the present disclosure, a first set of digitally controlled balancing electrodes applies a first static balancing voltage that produces a static electrostatic balancing force to lower the frequency f _H by? F + f ₀ . Thus, rather than an attempt to remove the frequency division Δf as previously known to simply lower the frequency f _H to match the frequency f _L, by balancing the electrodes of the first set of additional frequency offset to be applied to the high-frequency mode f _H f ₀ . According to the present disclosure, a second set of digitally controlled balancing electrodes are used to lower the frequency f _L by the same small frequency offset f ₀ . This shifts both the high frequency mode f _H and the low frequency mode f _L to a new frequency position where frequency balancing can now be applied by a small frequency offset f ₀ . Static balancing providing a Δf and f ₀ It is noted that it is very difficult and very non-linear (non-linear) is obtained exactly in the analog domain. The second set of balancing electrodes is also used to dynamically apply the fine balancing voltage to the finer frequency adjustment 隆 f obtained, as compared to the prior art frequency balancing scheme, which is now applied with respect to the frequency offset f ₀ . Dynamic fine balancing (performed in the analog or digital domain) uses the same second set of electrodes as is used to apply the small frequency offset f ₀ to the low frequency mode f _L. This ensures that the resolution of the dynamic balancing is improved regardless of the magnitude of the first static balancing voltage applied to eliminate the frequency division [Delta] f. This dynamic fine balancing can effectively counteract the motion imbalance that occurs during normal operation and lifetime of the gyroscope.

In various examples, the second set of capacitive balancing electrodes are arranged to apply a second static balancing voltage that is less than the first static balancing voltage applied by the first set of capacitive balancing electrodes. What the small frequency offset f ₀ means is that the frequency offset f ₀ is small when compared to the frequency splitting? F. Therefore, it will be understood that in many instances f ₀ < f, and preferably f ₀ < Since the dynamic fine balancing needs to be corrected only for the range of fluctuations expected during normal operation, the frequency offset f ₀ may be very small when compared to the frequency division Δf. In some examples, f ₀ is selected to be approximately less than Δf / 5, Δf / 6, Δf / 7, Δf / 8, Δf / 9, Δf / 10 or Δf / 10. The smaller the frequency offset f ₀ , the better the resolution. The usable range of the fine frequency adjustment ± δf is up to a maximum value equal to the frequency offset f ₀ .

In various examples, the second set of digitally controlled capacitive balancing electrodes is dynamically controlled to dynamically apply a fine balancing voltage that produces a dynamic electrostatic balancing force that provides a fine frequency adjustment < RTI ID = 0.0 > In some examples, the gyroscope is coupled to a second set of digitally controlled capacitive balancing electrodes and is adapted to dynamically control a second set of capacitive balancing electrodes to apply a fine frequency adjustment < RTI ID = 0.0 > And a control circuit. In some examples, the gyroscope is coupled to a second set of digitally controlled capacitive balancing electrodes and configured to provide an analog signal < RTI ID = 0.0 > And a control circuit. In various examples, the second set of capacitive balancing electrodes are independently controlled with the first set of capacitive balancing electrodes. For example, the gyroscope may include a digital control system arranged to control a second set of digitally controlled capacitive balancing electrodes independently of the first set of capacitive balancing electrodes. As discussed further below, the first and second sets of balancing electrodes may be physically identical except for their angular position.

In at least one example, the first set of capacitive balancing electrodes comprises four groups of balancing electrodes, the four groups being conformally spaced around the annular resonator, i. In general, the four groups each include n / 2 or n balancing electrodes. One or more balancing electrodes in each group are connected to each other to apply the same voltage. One of the balancing electrodes of these four groups is aligned with, crosses, or is adjacent to the axis of the high frequency mode f _H. For an example of the first cos 2? Excited along the major axis, each of the four groups has one or two balancing electrodes, i. E., All four or eight electrodes.

In at least one example, the second set of capacitive balancing electrodes comprises four groups of balancing electrodes, the four groups being conformally spaced around the annular resonator, i. In general, the four groups each include n / 2 or n balancing electrodes. One or more balancing electrodes in each group are connected to each other to apply the same voltage. One of the balancing electrodes of these four groups is aligned with, crosses, or is adjacent to the axis of the low frequency mode f _L. For an example of the second cos 2? Induced along the secondary axis, each of the four groups has one or two balancing electrodes, i.e., all four or eight electrodes.

For an example of cos 2 &thetas;, as described herein, the gyroscope uses potentially all 16 capacitive balancing electrodes to apply dynamic electrostatic balancing forces to an annular resonator while in prior art electrostatic balancing schemes 16 Only eight of the balancing electrodes are used at any one time.

In at least one embodiment, the drive electrodes are controlled independently of the first and / or second set of balancing electrodes. In some instances, the driving electrodes may be arranged to apply an analog excitation voltage. In some examples, the driving electrodes may be arranged to apply a digitally controlled excitation voltage. The set of capacitive driving electrodes may be coupled to an appropriate digital control circuit. The set of capacitive driving electrodes may be disposed inside or outside the annular resonator.

In one or more examples, the gyroscope further includes a set of capacitive sensing electrodes arranged to measure the induced second cos n? Resonance by sensing a voltage representing a second frequency f _S. This allows the gyroscope to determine the applied angular rate. In an open loop operation, the capacitive sense electrodes can directly sense the voltage representing the second frequency f _S. In closed loop operation, the capacitive sense electrodes may provide a feedback signal to disable the second cos θ resonance. The driving electrodes may thus comprise first and second driving electrodes. Such closed loop operation is well known and its content is incorporated herein by reference, for example as described in US 6,282,958. The set of capacitive sense electrodes can be placed inside or outside the annular resonator.

In various examples, a vibrating structure gyroscope may include a digital control circuit coupled to each set of capacitive electrodes. At least one digital control circuit may be coupled to the first set of capacitive balancing electrodes and at least one other digital control circuit may be coupled to the second set of capacitive balancing electrodes. The digital control circuits may be coupled to independently control the first and second sets of capacitive balancing electrodes. Each digital control circuit includes a digital-to-analog converter (DAC) arranged to generate balancing voltages, e.g., 8-bit (or higher, e.g., 16-bit) DAC, < / RTI >

In one or more examples, a first set of capacitive balancing electrodes is coupled to the DAC, and a second set of capacitive balancing electrodes is coupled to another independently controlled DAC. As described above, the first set may comprise four groups and each group may comprise two independently controlled balancing electrodes. In these examples, a first set of capacitive balancing electrodes is coupled to the first and second DACs. As also described above, the second set may comprise four groups and each group may comprise two independently controlled balancing electrodes. In these examples, a second set of capacitive balancing electrodes are coupled to the third and fourth DACs. In these examples there are four independently controllable DACs that allow the voltages applied to each of the four groups to be adjusted.

It can be appreciated that the angular position of the capacitive drive electrodes can be used to define the major axis. The angular position of each of the capacitive balancing electrodes may be defined relative to the major axis, for example at an angle of up to 360 [deg.] Or around 180 [deg.] Around the annular resonator. In some examples, the gyroscope includes groups of four balancing electrodes at angular positions equally spaced around the annular resonator, the four groups having N (e.g., < RTI ID = 0.0 > N = 16) capacitive balancing electrodes. One or more balancing electrodes of the four groups of balancing electrodes provide respective first and second sets of balancing electrodes. N capacitive balancing electrodes may be disposed inside and / or outside the annular resonator. Since there is a squared relationship between the balancing voltage and the frequency adjustment, the voltage applied in relation to the annular resonator, i.e. applied to the balancing electrode located inside or outside of the annular resonator, is positive or negative, Cognition is not important.

The N capacitive balancing electrodes may include N / 2 or N / 4 balancing electrodes equally spaced around the annular resonator to provide a first set of capacitive balancing electrodes that can be used to apply a static balancing voltage have. The N capacitive balancing electrodes include another N / 2 or N / 4 balancing electrodes equally spaced around the annular resonator to provide a second set of capacitive balancing electrodes that can be used to apply a fine balancing voltage can do. As described above, each of the first and second sets of capacitive balancing electrodes comprises four groups of balancing electrodes, and the four groups are equally spaced around the annular resonator, that is, at 90 [deg.] With respect to each other, do. Each group may comprise one, two or more balancing electrodes electrically connected together to apply the same voltage.

In some examples, the set of capacitive driving electrodes are arranged to apply a voltage that generates an electrostatic driving force to excite the first cos 2? Resonance along the major axis. In these examples, the gyroscope is made up of four groups with four balancing electrodes, the four groups having 16 capacitances at equally spaced angular positions around the annular resonator, spaced 90 [deg. Sex-balancing electrodes. In these examples, the first set of capacitive balancing electrodes is comprised of one or two of the four balancing electrodes in each of the four groups, and the second set of capacitive balancing electrodes is comprised of four Lt; RTI ID = 0.0 > and / or < / RTI > two balancing electrodes.

As can be understood from the discussion below, it is dynamically determined which one of the N balancing electrodes belongs to the first set and which belongs to the second set rather than a predetermined one. Of the N balancing electrodes, the four groups of balancing electrodes may belong to the first set or the second set at any given time instant. In some instances the gyroscope determines at any given time point which of the four groups of capacitive balancing electrodes provides the first set and which of the four groups of capacitive balancing electrodes provides the second set And a digital control system arranged to control the operation of the system. The first and second sets of balancing electrodes are mutually exclusive.

In some instances, the angular position alpha of the high frequency mode f _H for the primary axis may not change and then one of the four groups of capacitive balancing electrodes provides the first set and four of the capacitive balancing electrodes It does not matter which of the groups provides the second set.

In some instances, capacitive balancing electrodes used to eliminate frequency division may be determined at a given point in time of the life of a given gyroscope. This crystal can be varied depending on the angular position alpha of the high frequency mode f _H with respect to the main axis. The angular position α is a variable that can change depending on how the ring is physically deformed when compared to the theoretical case of the deforming annulus. The gyroscope may thus include a control system arranged to determine the angular position of the high frequency mode f _H with respect to the primary axis. The control system can determine which of the four groups of the N balancing electrodes provides the first set and the second set, respectively, at any given time instant based on the angular position a. In some instances, the first set of capacitive balancing electrodes is selected such that at least one of the four groups of balancing electrodes is aligned, crossed, or adjacent to the axis of the high-frequency mode f _H. In some examples, the second set of capacitive balancing electrodes are selected such that at least one of the four groups of balancing electrodes is aligned, crossed, or adjacent to an axis of the low-frequency mode f _L.

In some examples, the high-frequency mode f _H is aligned with the main axis to become alpha = 0. In these examples, the high and low frequency modes can be achieved by applying a static balancing voltage to the first set of balancing electrodes aligned with the primary axis, i.e., the balance, f _H ', is adjusted to f _L '. Alternatively, in these examples, the high and low frequency modes may be selected such that the static balancing voltage is within ± 11.25 ° of the cos 2θ resonance, eg, located at ± 90 ° / 4n across or adjacent the major axis with respect to the major axis , So that the balance, i.e., f _H ', is adjusted to f _L ' by applying it to the pair of balancing electrodes of the first set. This makes it possible to resolve the static electrostatic balancing force along the major axis.

In some instances, the high frequency mode fH is not aligned with the major axis, so that alpha has a non-zero value. In these examples, the high frequency mode f _H can be defined at an angle a with respect to the principal axis, the first frequency f _P and the second frequency f _S as follows:

And

In these examples, the high and low frequency modes can be achieved by applying a static balancing voltage to the first set of balancing electrodes aligned with the angular position alpha with respect to the major axis, i.e., f _H 'is adjusted to f _L ' . Alternatively, in these examples, the high and low frequency modes may have a static balancing voltage across the angular position alpha or adjacent thereto, e.g., +/- 90 deg. / 4n, e.g., +/- 11.25 deg. by applying a pair of balancing electrode of the set balance, i.e., f _H 'is f _L' being in line with, can be achieved.

For the case of α = 22.5 ° (2α = 45 °), the components of sin2α and cos2α are equal, so that both the main axis vibration and the secondary axis vibration resonate at the same intermediate frequency, (Due to the overlapping of the two modes). In this case the high frequency and low frequency modes are balanced by applying a fine balancing voltage to the second set of balancing electrodes located at 22.5 ± 45 °, or -22.5 ° or 67.5 °, from the main axis for cos 2θ resonance, ie, f _H ' Is maintained at f _L '.

In some instances, the high-frequency mode f _H is aligned with the secondary axis, resulting in α = 45 °. In these examples, the high and low frequency modes can achieve a balance, i.e., f _H 'is maintained at f _L ' by applying a static balancing voltage to the first set of balancing electrodes aligned with the secondary axis. Alternatively, in these examples, the high frequency and low frequency modes may be set such that the static balancing voltage crosses or is adjacent to the secondary axis with respect to the secondary axis, e.g., ± 90 ° / 4n, for example ± 11.25 The balance, i.e., f _H ', is maintained at f _L ' by applying the first set of balancing electrodes to the pair of balancing electrodes. It is possible to resolve the static electrostatic balancing force along the secondary axis.

One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying drawings, in which:
Figure 1 schematically shows the primary and secondary vibration axes for a Coriolis-type vibrating structural gyroscope;
Figure 2 shows the residual frequency division for a typical collision-type oscillatory structure gyroscope;
Figures 3A-3C schematically illustrate how electrostatic frequency balancing is implemented in a vibrating structural gyroscope according to the prior art;
Figures 4A-4D schematically illustrate how electrostatic frequency balancing is implemented in a vibrating structural gyroscope according to an example of this disclosure;
Figure 5 provides a first exemplary arrangement of capacitive electrodes in a vibrating structure gyroscope in which a pair of balancing electrodes straddle the drive axis;
Figure 6 provides a second exemplary arrangement of capacitive electrodes in a vibrating structural gyroscope in which the balancing electrode is aligned with the drive axis;
Figure 7 shows the balance frequency relationship for a digitally-controlled voltage;
Figure 8 shows frequency shift resolution as a function of dynamic frequency shift;

Having a first cos 2? Resonance 2 excited along the main axis P and a second cos 2? Resonance 4 coriolis-induced along the second axis S at 45 ° to the main axis P An annular resonator is schematically illustrated in Fig. In the case of a geometrically perfect resonator, there is no frequency division and no balancing is required. In practice, the incomplete geometry of the annular resonator unfortunately results in the first frequency f _P of the first cos 2? Resonance 2 being superimposed on the high frequency mode f _H and the orthogonal low frequency f _L.

Figure 2 shows an example of the reality for a silicon MEMS vibratory structure gyroscope with a first cos 2 [theta] resonance driven at a nominal frequency of 14 kHz. There is a division of 0.424 Hz between the frequencies of the high frequency mode (HFM) and the low frequency mode (LFM). In this example, α = 0 °.

The vibrating structural gyroscope according to the examples of this disclosure may comprise a capacitive electrode arrangement as shown in Fig. 5 or Fig. The annular resonator 6 is externally surrounded by a set of eight capacitive driving or sensing electrodes 8. The annular resonator 6 is surrounded internally by a set of 16 capacitive balancing electrodes 10 grouped into four sets. In Figures 5 and 6, the capacitive balancing electrodes 10 have different angular positions for the main axis P and the secondary axis S, but the control logic is the same. In operation, static or digitally controlled balancing voltages may be independently applied to any of four groups of sixteen capacitive balancing electrodes 10. The operation principle of such a gyroscope is disclosed, for example, in US 7,637,156, the contents of which are incorporated herein by reference in their entirety.

In the electrostatic frequency balancing scheme according to the prior art, the residual frequency division? F = f _H - f _L is Detected during the operation is (Fig. 3a), and is applied to a static balancing -Δf to match the f _H f lowers to _L (Fig. 3b). A first set of electrodes, i.e., a group of four of the sixteen electrodes shown in Figures 5 and 6, is used to apply a static balancing voltage. During the lifetime of the gyroscope, f _H and To deal with the deviation between f _L , f _H The dynamic balancing adjustment δf can be applied to the high frequency mode f _H to match f _L. However, when digitally controlling the voltage that generates the electrostatic balancing force to adjust the high frequency mode f _H , the resolution of the balancing effect decreases as the voltage difference increases.

In the electrostatic frequency balancing scheme according to one example of this disclosure, there is an additional offset balance applied prior to dynamic balancing, as shown in Figs. 4A-4D. As before, the residual frequency division? F = f _H -f _L Detected during the operation is (Fig. 4a), and is applied to a static balancing -Δf to match the f _H f lowers to _L (Fig. 4b). A first set of electrodes, i.e., a group of four of the sixteen electrodes shown in Figures 5 and 6, is used to apply a static balancing voltage. In the new static balancing step of Fig. 4 (c), the first set of electrodes are used to adjust the frequency f _H to an offset frequency f _H 'below the frequency f _L , i.e., f _H ' = (f + f ₀ ) The offset f ₀ is applied. The electrodes of the second set, that is, the sixteen electrodes of four other groups shown in Figs. 5 and 6, is used to apply the same frequency offset f ₀ to lower the low-frequency mode f _L, a frequency f _L is also Is reduced to the offset frequency f _L ', i.e., f _L ' = (f _L -f ₀ ) by the same frequency offset f ₀ . The frequency offset f ₀ is smaller than the frequency division. Following the dynamic balancing step in Figure 4d, dynamic balancing provides a fine frequency adjustment ± f applied to the offset frequency f _L 'to keep f _L ' at f _H '. This fine frequency adjustment ± f is applied to the second set of electrodes likewise. The fine frequency adjustment ± δf can have any value up to the maximum of the frequency offset f ₀ . This fine dynamic balancing can be performed in the analogue domain as a small signal approximation can be applied if the trim is sufficiently fine. This electrostatic frequency balancing scheme uses at least two groups of four of the sixteen electrodes shown in Figures 5 and 6, i.e. at least eight balancing electrodes, and when each group of four includes pairs of electrodes , Generally all 16 of the balancing electrodes are used.

In the embodiment shown in Figure 5, there is a pair of balancing electrodes ESB-11.25 and ESB11.25 straddling the main axis P, i. E. Electrodes ESB-11.25 and ESB11.25, Each adjacent a main axis P. This is a pair in a group of four electrodes used to apply the same balancing voltage. For cos 2 &thetas;, if < RTI ID = 0.0 > a = 0, < / RTI > the static balancing voltage is applied to a pair of balancing electrodes of the first set at +/- 11.25 degrees with respect to the principal axis. Both smaller static balancing voltages for the frequency offset f ₀ and fine balancing voltages for the fine frequency adjustment ± f are applied to the other pair of balancing electrodes (ESB 33.75 and ESB 56.25) across the secondary axis S That is, each of the electrodes ESB33.75 and ESB 56.25 is adjacent to the secondary axis S. In other words, this is a pair in a group of four electrodes providing the second set.

In the example shown in Fig. 6, there is a balancing electrode ESB0 aligned with the main axis P. This is one in the group of four electrodes used to apply the same balancing voltage. For < RTI ID = 0.0 > cos = 2 < / RTI > resonance, a static balancing voltage is applied to the first set of balancing electrodes aligned with the main axis. Both the smaller static balancing voltages for the frequency offset f ₀ and the fine balancing voltages for the fine frequency tuning ± f are applied to another balancing electrode ESB 45 aligned with the secondary axis S. In other words, this is one in the group of four electrodes providing the second set.

More generally, it is in the operating mode of the gyroscope α position, i.e., the high-frequency mode f _H relative to the main axis is a digital control system for determining the angular position α,. Once the mode position a is known, a group of aligned (or crossed or adjacent) electrodes with the high frequency mode f _H is used to provide a first set for static balancing. The second set of electrodes are therefore different groups of electrodes to be aligned (or intersecting or adjacent to) the low frequency mode f _L. Referring to Figures 5 and 6, which of the 16 balancing electrodes is designated as the first set and which is designated as the second set is dynamically determined according to the mode position? At a given point within the lifetime of the gyroscope.

example

In this illustrative example, the vibratory structure gyroscope has a first cos 2? Resonance excited at a first frequency f _p of 14 kHz and has a residual frequency division? F = 8 Hz. According to the electrostatic balancing scheme shown in Figures 4a to 4d, the 8Hz static balance (Fig. 4b), f ₀ = 0.1Hz the frequency offset is small (Fig. 4c) is applied, and the dynamic balance is fine frequency shown by ± δf A fine balancing voltage is allowed for regulation (Figure 4d). The fine frequency adjustment δf may have a value up to f ₀ , that is, δf = ± 0.1 Hz or less, for example, δf = ± 0.05 Hz or δf = ± 0.01 Hz.

For a DAC whose DAC value is n (LSB), the DAC output voltage V (n) = kN. The DAC can control the balancing voltage from 0V to V ₀ as n varies from 0 to 2 ^N , where N is the number of DAC bits, that is, the 8-bit DAC has N = 256. The balancing efficiency η _B is related to the voltage difference ΔV = V ₀ -V (n) by a squared relationship, ie η _B depends on ΔV ² . For the example where n = 12 and V ₀ = 10V, η _B = 10ΔV ² / Hz.

The sensitivity to the change of n, that is, the resolution, is as follows.

This indicates that resolution is a function of n, so that finer resolution is achieved when n is small.

7, the point A (small n) on the graph represents the dynamic frequency balance adjustment δf = ± 0.05 Hz with respect to the static balance of 8 Hz according to FIG. 3c, while the area B (large n) According to 4d, the dynamic frequency balance adjustment δf = ± 0.05 Hz with respect to the frequency offset f ₀ of 0.1 Hz. Figure 8 shows how finer the resulting frequency shift resolution is for B compared to A. The improvement in resolution is 8.81.

This example illustrates that when the dynamic balance adjustment is implemented in conjunction with a relatively large static balance correction, e. G. 8 Hz, the available resolution is degraded, which limits overall gyroscopic performance (Figure 3) . On the other hand, according to FIG. 4, the additional frequency offset f ₀ = 0.1 Hz applied to both the high and low frequency modes ensures that the resolution of the dynamic frequency balance adjustment is maintained independent of the initial static balance. This provides improvements in a wide range of different gyroscopes.

Claims (15)

An annular resonator arranged to vibrate in plane in response to the electrostatic driving forces;
Excites the first cos n? Resonance along the major axis at the first frequency f _p so that a Coriolis force resulting from the applied angular rate about the out-of-plane axis is transmitted along the second axis at the second frequency f _s to the second a set of capacitive driving electrodes arranged to apply a voltage to induce cos n? resonance, which generates an electrostatic driving force;
The geometry of the annular resonator is superimposed on the high frequency mode f _H and the orthogonal low frequency mode f _L , resulting in a first frequency f _P having a frequency division? F defined by? F = f _H -f _L ,
A first static balancing to generate a static electrostatic balancing force to lower the frequency f _H by an offset frequency f _H 'below the frequency f _L by a small frequency offset f ₀ , i.e., f _H ' = f _H -? F - f ₀ , A first set of capacitively balancing electrodes that are arranged to apply a voltage and are digitally controlled; And
To apply a second static balancing voltage that produces a small static electrostatic balancing force to lower the frequency f _L by an offset frequency f _L ', i.e., f _L ' = f _L -f ₀ , by the same small frequency offset f ₀ A vibrating structure gyroscope comprising a second digitally controlled set of capacitive balancing electrodes,
Capacitive balancing electrode of the second set of operations when f _H 'a _L f' the frequency offset by f _H to hold 'the fine adjustment frequency to lower

Wherein the dynamic balancing voltage is dynamically applied to generate a dynamic balancing force that provides a dynamic balancing force to provide a dynamic balancing force. The vibratory structure gyroscope according to claim 1, wherein the small frequency offset satisfies f ₀ <? F and preferably satisfies f ₀ << Δf. 6. A vibratory structural gyroscope as claimed in any one of the preceding claims, comprising a digital control system arranged to control the second set of capacitive balancing electrodes independently of the first set of capacitive balancing electrodes. 6. A vibratory structural gyroscope as claimed in any one of the preceding claims, comprising a control system arranged to determine an angular position alpha of the high-frequency mode f _H relative to the primary axis. 5. The apparatus of claim 4, comprising N capacitive balancing electrodes, wherein the digital control system is operable to determine which of the four groups of balancing electrodes among the N capacitive balancing electrodes is at the angular position alpha at any given time instant Based on the first set and the second set, respectively. The method according to claim 5, wherein at least any one of said four groups of the capacitive balancing electrodes are balanced electrode of the first set or arranged (aligned) to the axis of the high-frequency mode f _H, this crossing or (straddling) or in Wherein the vibration structure is selected to be adjacent. Claim 5 or according to 6, wherein the capacitive balancing electrode of the second set or at least any one of said four groups of balance electrodes are arranged (aligned) to the axis of the low frequency mode f _L, this crossing or (straddling) Or adjacent to, a vibrating structural gyroscope. 6. A method according to any one of the preceding claims, further comprising the steps of: dynamically controlling the second set of capacitive balancing to be connected to the second set of digitally controlled capacitive balancing electrodes and to provide the fine tuning &lt; RTI ID = 0.0 &gt; And an analog signal control circuit disposed therein. 6. A method according to any one of the preceding claims, comprising a digital control circuit coupled to said second set of digitally controlled capacitive balancing electrodes, said digital control circuit comprising a digital &lt; RTI ID = _0.0 &gt; And a digital-to-analog converter (DAC) arranged to generate a controlled voltage. 10. The method of claim 9, wherein the digital control circuit coupled to the second set of digitally controlled capacitive balancing electrodes is configured to dynamically control the second set of capacitive balancing electrodes to provide the fine frequency adjustment &lt; RTI ID = 0.0 &gt; , Wherein the vibrating structural gyroscope comprises: 6. A method as claimed in any one of the preceding claims, comprising a digital control circuit coupled to the first set of digitally controlled capacitive balancing electrodes, the digital control circuit generating the first static balancing voltage And a digital-to-analog converter (DAC) arranged to generate a digitally controlled voltage. 6. The vibratory structure gyroscope according to any one of the preceding claims, further comprising a set of capacitive sensing electrodes arranged to measure the induced second cos n [theta] resonance. 6. A vibratory structure gyroscope according to any one of the preceding claims, wherein the set of capacitive driving electrodes is arranged to apply a voltage that generates an electrostatic driving force to excite a first cos 2? Resonance along the primary axis. 14. The device of claim 13, comprising 16 capacitive balancing electrodes in angular positions equally spaced about the annular resonator in four groups of four balancing electrodes, the four groups being spaced 90 degrees apart from each other Vibration structure gyroscope. 15. The method of claim 14, wherein the first set of capacitive balancing electrodes comprises one or two of the four balancing electrodes in each of the four groups, and the second set of capacitive balancing electrodes comprises the four groups And one or more of the four balancing electrodes in each of the two balanced electrodes.

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